DEVONIAN 283 



forms the country rock, as in the Yukon as well as the larger confluent 

 stream, the river valleys are narrow, with walls rising steeply from close 

 to the water's edge. The smaller tributaries occupy A— shaped gorges. 

 Alany small castellated peaks and pinnacles break the contour of the val- 

 ley slope, giving an irregular topography along the watercourses. This 

 irregularity is not carried back into the interstream .areas because of the 

 general beveling to which the uplands have been subjected in a previous 

 cycle. 



Fossils Avere found at a number of localities in the limestones. At 

 some exposures opposite the mouth of Woodchopper creek and about 1 

 mile farther up the Yukon the following fauna occurs in limestones inter- 

 bedded with tuffs : 



Devonian Fossils ohtalnecl near Woodchopper^ 



CijatltopJti/lhim sp. Aiioplotlicca ? coiicava (Hall). 



Crinoid stems. Dalmaiiella sp. 



Stropheodonta cf. cah-iiii Miller. Spirifer sp. 



Camarotoechia, small sp. Renssela'ria ? sp. 



Atrypa reticularis Linu. Cypricardinia sp. 



Atrypa cf. flaiellata Goldf. Gonocardium sp. 



Schizophoria striatula (Schlotheim). Actinopteria near pcrstrialis Hall. 



Anihocwlia cf. umbonata (Com-ad). Pleurotomaria sp. 



Sigaretus ? n. sp. 



This is the same fauna and horizon as that occurring at the mouth of 

 Salmontrout river on the Porcui^ine (see page 327). Atrypa cf. ffahcl- 

 lata is one of the most abundant species in both faunas. The very pecu- 

 liar gasteropod here referred doubtfully to Sigaretus and Stroplieodonta 

 cf. calvini are also common to botli. 



About 2 miles below AVoodchopper creek the igneous beds which are 

 there the predominant rocks are interrupted by a cliif of bluish gray 

 Devonian limestone rising 200 feet al)ove the river. Fossils are very 

 scarce here. The following species were obtained: 



Crinoid stems. Stropheodonta sp. 



Atrypa reticularis. Gonocardium sp. 



Camarotoechia sp. 



The base of the Devonian section is not exposed on the Yukon, but the 

 limestone on the Porcupine, which the faunas pretty clearly indicate to 

 be the stratigraphic equivalent of the limestone beds near Woodchopper, 

 is known to rest directly on the Silurian. Both of these faunas appear to 



'" It is proposed to describe fuHy and to illustrate the Devonian and Silurian faunas 

 listed in this paper in a subsequent paper, when the paleontologic determinations will 

 be subject to revision, with the aid of more complete collections. 



